The Research Of Gold And Silver Leaching From Printed Circuit Boards By Hydrometallurgical Technology

With the popularization of electronic products and the accelerating pace of updates, a lot of electronic wastes - printed circuit boards are also increasing at an alarming rate. As the PCBs are harmful to environment, even to human body, and containing copper, gold, silver and other metal resources, it attracts more and more attention for the recycling of resources and becomes the recently studying hot spot. Therefore, it was impertative to develop an economical, effective and environmental friendly technology for hydrometallurgical recycling gold and silver from WEEE.The paper used waste computer printed circuit boards as the object of study. The PCBs were grinded and polished firstly, and the part of below 200 mesh was pretreatmented using nitric acid, and dried the residue for being digested after pretreatment. The contents of gold and silver of waste computer circuit boards were 0.0545 mg/g and 0.281 mg/g, respectively. Three leaching methods were chosen to leach gold and silver in the article, and the best leaching condition of the three methods were:(1) Thiocyanate leaching gold and silver with hydrogen peroxide existed:under neutral condition, solid/liquid ratio of 1:20, SCN" concentration of 0.8 mol/L, adding 7.5%(v/v) hydrogen peroxide with the concentration of 30%, leaching temperature of 20℃, leaching time of 1 h, and the highest leaching rate of gold and silver reached 88.37% and 78.43%, respectively; (2) Ammonia leaching gold and silver with copper and ammonia existed:solid/liquid ratio of 1:60, ammonia concentration of 25%-28% (w/w), Cu2+ concentration of 3×10-2 mol/L, and adding (NH3)2SO4 with finite concentration to make the pH value of 9-10, leaching temperature of 60 ℃, leaching time of 4 h, and the highest leaching rate of gold and silver reached 96.23% and 92.58%, respectively; (3) Iodinate method leaching gold and silver:solid/liquid ratio of 1:50, pH value of 8-9, potassium iodide concentration of 0.2 g/mL, mass ratio of m(I2):m(KI)=l:8, ammonia volume ratio of 1%, leaching temperature of 20℃, leaching time of 1 h, and the highest leaching rate of gold and silver reached 96% and 88.24%, respectively.Thiocyanate gold and ammonia leaching gold and silver were selected to calculate the cost, comparing the two methods, thiocyanate leaching with the exists of hydrogen peroxide involved the lowest cost. Taking thiocyanate for economic benefit analysis, it was concluded that the profit gained from a ton of WPCB by this method was 180.4 yuan. Thiocyanate leaching gold and silver had the advantages of quick leaching speed, low toxicity, low cost, etc. Besides, it happened in the neutral condition, had weak corrosion to equipment and good environmental and economic benefits, which meets the trend of development for the environmental ptotection and resource recycled in the modern times.